In a conventional rotary engine the oil reservoir is positioned between the rotating cylinders. Centrifugal force tends to draw the lubricating oil into the combustion chamber. This was the primary drawback of the French Ghome engine in the first world war. In addition to smoking, consumption of oil could cause engine failure. This ongoing problem of oil seepage has greatly limited the use of the relatively light weight rotary engine.
In aviation particularly, there is a need great need for a reliable engine having a low weight: power ratio. Anything that can be done to reduce this weight: power ratio should be done. In helicopters, where every pound of load must be monitored because of high fuel costs, there is a particular need for an engine having a low weight: power ratio.